Aqueous Reactions Aqueous Reactions and Solution and Solution

StoichiometryStoichiometry

► Aqueous Solutions – Aqueous Solutions – a solution which a solution which water is the solventwater is the solvent

► Solution = Solute + Solution = Solute + SolventSolvent

► Solute = smaller Solute = smaller part being dissolvedpart being dissolved

► Solute = larger Solute = larger fraction doing the fraction doing the dissolvingdissolving

►Molarity is used to Molarity is used to express conc. express conc.

MolarityMolarity

►M = moles of solute/ liters of solutionM = moles of solute/ liters of solution►A 0.38g sample of sodium nitrate is A 0.38g sample of sodium nitrate is

placed in a 50.0 ml volumetric flask placed in a 50.0 ml volumetric flask and is filled with water to the mark. and is filled with water to the mark. What is the molarity of the solution?What is the molarity of the solution?

MolarityMolarity

►How many grams of How many grams of potassium potassium permanganate are permanganate are needed to prepare needed to prepare 2.0 liters of a 0.2 2.0 liters of a 0.2 molar solution of molar solution of the salt?the salt?

Dilution ProblemsDilution Problems

►M1V1= M2V2M1V1= M2V2►How many liters of 12 molar sulfuric How many liters of 12 molar sulfuric

acid is necessary to make 2 liters of a acid is necessary to make 2 liters of a 6 molar conc. of the acid?6 molar conc. of the acid?

Specific Gravity or Density Specific Gravity or Density ProblemsProblems

►Commercially available conc. HCl is in Commercially available conc. HCl is in a aq sol cont 38% HCl by mass. D = a aq sol cont 38% HCl by mass. D = 1.19g/ml a) what is the molarity of the 1.19g/ml a) what is the molarity of the solution? b) how many ml of conc HCl solution? b) how many ml of conc HCl are required to make 1.00 l of a 0.10 are required to make 1.00 l of a 0.10 molar solution?molar solution?

ElectrolytesElectrolytes

► Solutes that separate Solutes that separate into tow or more ions into tow or more ions when dissolved in when dissolved in water are called water are called electrolytes.electrolytes.

► Solutes that remain Solutes that remain uncharged molecules uncharged molecules are called non-are called non-electrolytes.electrolytes.

► Either may be Either may be soluble in water.soluble in water.

ElectrolytesElectrolytes►NaClNaCl(s)(s) Na Na+ + + Cl- ionic solids + Cl- ionic solids

dissociate into ions.dissociate into ions.►Electrical ConductivityElectrical Conductivity Strong electrolytes conduct electricity veryStrong electrolytes conduct electricity very well because ions totally dissociatewell because ions totally dissociate Weak electrolytes only weakly conductWeak electrolytes only weakly conduct because ions only partially dissociatebecause ions only partially dissociate Nearly all ionic cmps are strong and Nearly all ionic cmps are strong and

molecular cmps are usually non-molecular cmps are usually non-electrolyteselectrolytes

Acids, Bases, And SaltsAcids, Bases, And Salts

► Acids – are solutes Acids – are solutes that can ionize to that can ionize to produce hydrogen produce hydrogen ionsions

H+(aq)H+(aq)► Strong acids Strong acids

dissociate and exist dissociate and exist almost totally as ionsalmost totally as ions

► Ex HClEx HCl(aq) (aq) HH+ + + + ClCl--

Weak AcidsWeak Acids

►HCHC22HH33OO2 2 HH+ + + C+ C22HH33OO2-2- Weak acids only partiallyWeak acids only partially dissociate the double arrows dissociate the double arrows

indicate that the reaction indicate that the reaction occurs in significant occurs in significant amounts in both directionsamounts in both directions

Acedic Acid or Vinegar is the Acedic Acid or Vinegar is the classic example.classic example.

Acids Cont.Acids Cont.

►H+ is simply a proton – acids are often H+ is simply a proton – acids are often called proton donorscalled proton donors

►Monoprotic acids – contribute one H+ Monoprotic acids – contribute one H+ per molecule of acid ex. HCl or HNOper molecule of acid ex. HCl or HNO33..

►Diprotic acids contribute two H+ per Diprotic acids contribute two H+ per moleclue ex. Hmoleclue ex. H22SOSO44

►Polyprotic acids contribute greater Polyprotic acids contribute greater than one H+ ex. Hthan one H+ ex. H22SOSO4 or 4 or HH33POPO44. .

BasesBases

►Are substances that accept H+ ions or a Are substances that accept H+ ions or a proton.proton.

►Ex HEx H+(aq)+(aq) + OH- + OH-(aq)(aq) H H22OO(l)(l)

►Ex HEx H+(aq)+(aq) + NH + NH3-((aq) 3-((aq) NHNH4(aq)4(aq)

►OH- & NHOH- & NH3- 3- are the bases. OH- is the are the bases. OH- is the most common base in aqueous most common base in aqueous solution. Sometimes bases are defined solution. Sometimes bases are defined as substances with increased OH- ions as substances with increased OH- ions in solution.in solution.

NoteNote

► Acids and bases are electrolytes – if a strong Acids and bases are electrolytes – if a strong acid or base they are strong electrolytes if a acid or base they are strong electrolytes if a weak acid or base a weak electrolyte. weak acid or base a weak electrolyte.

► Strong Acids Strong Acids

HCl (aq) Hydrochloric HHCl (aq) Hydrochloric H22SOSO4 4 SulfuricSulfuric

HNOHNO3 3 (aq) Nitric HBr Hydrobromic(aq) Nitric HBr Hydrobromic

HClOHClO4 4 (aq) Prechloric HI Hyrooiodic(aq) Prechloric HI Hyrooiodic

HClOHClO3 3 (aq) chloric(aq) chloric

►Weak AcidsWeak Acids

HF Hydrofluoric HF Hydrofluoric

HH22CC22HH33OO2 2 AcedicAcedic►Strong basesStrong bases

Grp I HydroxidesGrp I Hydroxides

LiOH, NaOH, KOH, RbOH, and CsOHLiOH, NaOH, KOH, RbOH, and CsOH

Grp II HydroxidesGrp II HydroxidesCa(OH)Ca(OH)2, 2, Sr(OH)Sr(OH)2, 2, Ba(OH)Ba(OH)22

Weak Base NHWeak Base NH3 3 AmmoniaAmmonia

SaltsSalts

► Are ionic compounds Are ionic compounds formed from acids formed from acids by the replacement by the replacement of one or more H+ of one or more H+ ions with some other ions with some other cation.cation.

► For example For example replacing the H+ ion replacing the H+ ion in HCl(aq) with Na+ in HCl(aq) with Na+ ion yields NaCl.ion yields NaCl.

Identifying strong and weak Identifying strong and weak electrolyteselectrolytes

►most salts are most salts are strong electrolytesstrong electrolytes

►most acids are weak most acids are weak electrolytes except electrolytes except for the strong acidsfor the strong acids

► most strong bases most strong bases hydroxides of hydroxides of metals are strong metals are strong electrolytes except electrolytes except NHNH33 which is a weak which is a weak base and electrolyte base and electrolyte

►Neutralization reactions are those between Neutralization reactions are those between an acid and a base they yield salt and wateran acid and a base they yield salt and water

► Ionic EquationsIonic Equations

a. varying amounts of detail can be included a. varying amounts of detail can be included in chem eq depending on what information is in chem eq depending on what information is relevant to the problem at handrelevant to the problem at hand

b. molecular equations - have all the species b. molecular equations - have all the species written as associated molecules even though written as associated molecules even though they may be disassociatedthey may be disassociated

c. complete ionic eq – strong electrolytes are c. complete ionic eq – strong electrolytes are written as dissociated ions; molecules, solids, written as dissociated ions; molecules, solids, and weak electrolytes are written as and weak electrolytes are written as associated ionsassociated ions

d. net ionic equations – an ionic eq in d. net ionic equations – an ionic eq in which the spectator ions have been which the spectator ions have been cancelled. cancelled.

►Rules for Converting Molecular eq to IonicRules for Converting Molecular eq to Ionic

1. Ionic Sub indicated as dissolved in 1. Ionic Sub indicated as dissolved in solution such as NaClsolution such as NaCl(aq) (aq) are normally are normally written as ionswritten as ions

2. Ionic substances that are insoluble (do 2. Ionic substances that are insoluble (do not dissolve readily) either as reactants not dissolve readily) either as reactants or products (precipitates) are rep as or products (precipitates) are rep as formulas of the compoundsformulas of the compounds

d. Molecular substances that are strong d. Molecular substances that are strong electrolytes such as strong acids are electrolytes such as strong acids are written as ions.written as ions.

e. Molecular substances that are weak e. Molecular substances that are weak electrolytes are represented as their electrolytes are represented as their molecular formulasmolecular formulas

f. Spectator ions – ions in an equation f. Spectator ions – ions in an equation that do not take part in the equation that do not take part in the equation are cancelled from both sides of the are cancelled from both sides of the equationequation

ExamplesExamples

►Ba(CBa(C22HH33OO22))2 2 + K+ K22CrOCrO4 4

►Ba(CBa(C22HH33OO22))2 2 + K+ K22CrOCrO4 4 BaCrO BaCrO4 4 + + 2KC2KC22HH33OO22

Ba + 2CBa + 2C22HH33OO2 2 + 2K + CrO+ 2K + CrO4 4 BaCrO BaCrO4 4 + 2K + 2K +2 C+2 C22HH33OO22

Ba + CrOBa + CrO4 4 BaCrO BaCrO44

ExamplesExamples

►Ca(CCa(C22HH33OO22))2 2 + H+ H22CC22OO44

►Ca(CCa(C22HH33OO22))2 2 + H+ H22CC22OO44 CaC CaC22OO4 4 + + HCHC22HH33OO22

►Ca+ 2CCa+ 2C22HH33OO2 2 + H+ H22CC22OO44 CaC CaC22OO4 4 + + HCHC22HH33OO22

►Weak acids do not splitWeak acids do not split

ExamplesExamples

►NHNH44NONO3 3 + NaOH + NaOH

► NHNH44NO3NO3 + NaOH + NaOH NH NH44OH + Na + NOOH + Na + NO3 3

►NHNH4 4 ++ NONO3 3 + Na + OH + Na + OH NHNH33 + H + H22OO + + Na Na

+ NO+ NO33

► NHNH4 4 + OH + OH NH NH33 + H + H22OO

Metathesis ReactionsMetathesis Reactions►Reactions in which two ionic reactants Reactions in which two ionic reactants

exchange ion partners exchange ion partners ►AX + BY AX + BY AY + BX AY + BX►Precipitation reactions are those Precipitation reactions are those

metathesis reactions in which an metathesis reactions in which an insoluble solid product or precipitate insoluble solid product or precipitate formsforms

A. Precipitate –insoluble solid productA. Precipitate –insoluble solid product B. Solubility – the amount of a B. Solubility – the amount of a

substance that can dissolve in a given substance that can dissolve in a given amount of solventamount of solvent

► (expressed in g/100 ml or in liters/mol) A (expressed in g/100 ml or in liters/mol) A substance is considered insoluble if its substance is considered insoluble if its solubility is less that 0.01 mol/l.solubility is less that 0.01 mol/l.

► Predicting solubility is a matter of know the Predicting solubility is a matter of know the solubility rules (Table 4.3 or what I should solubility rules (Table 4.3 or what I should know for AP list)know for AP list)

► Some metathesis reactions from water or Some metathesis reactions from water or another weak electrolyte or non-electrolyte another weak electrolyte or non-electrolyte in ionic and net ionic equations (appear as in ionic and net ionic equations (appear as associated species)associated species)

► Some methesis reactions form gases these Some methesis reactions form gases these are usually binary compounds of non-metals are usually binary compounds of non-metals exam ples Hexam ples H22S, COS, CO2, 2, HCN.HCN.

Redox It’s electro-magic Redox It’s electro-magic

► I. Oxidization I. Oxidization NumbersNumbers

A. Oxidization – loss ofA. Oxidization – loss of

electrons. LEOelectrons. LEO

B. Reduction – gain of B. Reduction – gain of electrons – GERelectrons – GER

C. When one reactant C. When one reactant loses e’s another loses e’s another reactant must gain reactant must gain themthem

Intro to electrochemistryIntro to electrochemistry

► D. reactions in which D. reactions in which electrons are trans are electrons are trans are called oxidization – called oxidization – reduction or redox reduction or redox reactionsreactions

► E. oxidization number E. oxidization number (ON) rules(ON) rules

1. atoms in the 1. atoms in the elemental form – elemental form – oxidization # = 0oxidization # = 0

2. monatomic ions – the 2. monatomic ions – the oxidization # = the oxidization # = the charge of the ioncharge of the ion

ex Naex Na++ = 1 S = 1 S-2 -2 = -2 = -2

3. non-metals usually 3. non-metals usually have neg ON although have neg ON although they can sometimes be they can sometimes be positivepositive

a> Oxygen usually =a> Oxygen usually =

-2 except peroxides-2 except peroxides

OO22-2 -2

= each O = -1 = each O = -1

b) hygrogen usually = +1 when bonded b) hygrogen usually = +1 when bonded to non-metals = -1 when bonded to to non-metals = -1 when bonded to metalsmetals

c) Fluorine = -1 in all cmps – halogens = c) Fluorine = -1 in all cmps – halogens = -1 in most binary cmps but when -1 in most binary cmps but when combine with oxygen as in oxyanions combine with oxygen as in oxyanions they have a + numberthey have a + number

4. The sum of oxidizations #’s 4. The sum of oxidizations #’s

a) in a neutral cmp = 0a) in a neutral cmp = 0

b) in a polyatomic ion = charge of ionb) in a polyatomic ion = charge of ion

Work sample exercise 4.6Work sample exercise 4.6